Flux should make things much easier. Also get the thinnest solder you can buy. 0.5 or 0.6.
You can do this with the mainboard on. Removing it would be overkill but if you are comfortable with it, suit yourself.
I'd use Thermal Grizzly Kryonaut, Arctic MX-4 or Mastergel. Just a good, regular, nonconductive thermal compound.
And get a magnifying glass with built in light and the smallest iron tip possible. Some may not need it, but it's still very good to have.
p.s. I'm talking about Core. The Lite I wouldn't try to do myself.
I've got a lite. Wish me luck. Seriously though, I've been practicing for the last couple of months. Got some 0.5 solder, MX4, and a soldering iron with nice fine tip. I'm comfortable with the kit I've got and the temps I'm working with so fingers crossed. :-)